It’s a message we hear over and over: Eat more fruits and vegetables, and cut back on sugar and fat. But adopting a healthier diet could have some unintended consequences. According to a new study, switching from a typical American diet to one recommended by the U.S. Department of Agriculture (USDA) would increase food-related greenhouse gas emissions.

Food production puts a huge strain on the environment. For instance, 17 to 32 percent of the world’s greenhouse gas emissions arise from farming and related activities such as fertilizer production. At the same time, more than two-thirds of Americans are overweight, and many of them have unhealthy eating habits.

So what would happen if people substituted apples and broccoli for candy bars and ice cream? The study authors compared Americans’ current diets to the USDA’s 2010 dietary guidelines and found that people were eating too much meat, eggs, solid fat, and added sugar and not enough fruit, vegetables, dairy products, and seafood. If Americans continued consuming the same number of calories per day but shifted toward the healthier mix of food recommended by the USDA, greenhouse gas emissions would rise by 12 percent, the team estimates.

What if people cut their calories? If Americans reduced their typical food intake from the current 2,534 calories to the recommended 2,000 calories per day without changing the type of foods consumed, one would expect associated greenhouse gas emissions to also fall by about a fifth. But if people cut their calories and simultaneously adopted the healthier USDA guidelines, emissions would fall by only 1 percent. That’s partly because reducing fat and sugar doesn’t have much effect on emissions, the authors say. And while people would be eating less meat, their dairy consumption would go up. “[T]his result speaks to the need to incorporate the environmental costs of food production into dietary recommendations,” the team concludes. — Roberta Kwok | 11 September 2014